Variable pitch impellers and closure seals therefor



Oct. 18, 1960 G. R.- TOTHILL 2,956,739

VARIABLE PITCH IMFELLERS Am: CLOSURE-SEALS THEREFOR Filed Feb. 15. 1957s Shets-Sheet 1 INVENTOR I GORDON ROY TOTHILLI B 237W Patent Agent Oct.18, 1960 s. R. TOTHILL 2,956,739

VARIABLE PITCH IMPELLERS AND CLOSURE SEALS THEREFOR Filed Feb. 13, 19575 Sheets-Sheet 2 97/ as 94 as 87 (0! 99 2 95 84 5 INVENTOI? 98 6 co oowROY Tqrmu.

Y R a tent Agent Get. 18, 1960 s. R. TOTHILL 2,956,739

VARIABLE PITCH IMPELLERS AND CLOSURE SEALS THEREFOR Filed Feb. 13, 19575 Sheets-Sheet 3 IIIII.

65 ea 27 e9 1 .4. 71 F3 56 ILL a INVENTOP 11' GORDON ROY ran-nu.

. R}-'-IW Pafen i Agent Oct. 18, 1960 G. R. TOTHILL 2,956,739 VARIABLEPITCH IMPELLERS AND CLOSURE sms THEREFOR Filed Feb. 13. 1957 44 sSheets-Sheet 4 JNVENTOI? GORDON ROY TOTHILL Pafen t Agerz t Oct. 18,1960 s. R. TOTHILL 2,956,739

VARIABLE PITCH IMFELLERS AND CLOSURE SEALS THEREFOR Filed Feb. 15. 19575 Sheets-Sheet 5 INVFNTOP GORDON ROY TOTH/LL By Q.B.?Lapk rma-' PazentAgent VARIABLE PITCH IMPELLERS AND CLOSURE SEALS THEREFOR Gordon RoyTothill, 118 Park St., Chatham, Ontario, Canada Filed Feb. 13, 1957,Ser. No. 639,879

6 Claims. (Cl. 230-270) This invention relates to variable-pitchimpellers and blade sealing arrangements, and more especially relates toimpellers or propellers whose blade pitch is automatically varied inaccordance with the idle or rotating condition of the impeller.

According to the invention an impeller system may be realized for use inassociation with an apertured housing, wherein the blades themselvesform shutters or closures for the aperture when the blades are notrotating, and wherein automatic pitch adjustment means respond when theblades are rotated to open the blading.

It is a primary object of the invention to provide an impeller systemsuch that the blades assume a minimum or reference pitch whenstationary, and when rotated by a powered means have an increase inpitch automatically effected to a predetermined maximum, which maximumpitch is held in accordance with angular acceleration forces andaerodynamic loading of the blading.

Another object of the invention is to provide an apertured enclosure andmulti-bladed impeller or propeller coaxial therewith and of such formthat in the minimum pitch condition of the blades the flow of gas orfluid through the aperture is prevented, without the use of check valvesor shutters.

A further object is to provide a simple, light, compact and durablepitch changing mechanism for a system of blading which is economical ofmanufacture and easy of assembly.

Yet another object is to provide -a sturdy blade pitch adjustingmechanism, characterized by a large mechanical advantage, adapted to beentirely housed within an impeller or propeller hub of relatively smalldiameter, and characterized further by a minimum of working parts.

Still another object is to provide a pitch-adjusting mechanism enclosedwithin a hub body which gradually effects an opening of bladesjournalling in the body from a closed position on starting and whichdraws no power from the driving source when the impeller or propellerhas reached an equilibrium speed of rotation.

A further major object is the provision of a pitchadjusting mechanismcapable of applying a large turning moment to each blade and inherentlycapable of taking up frictional wear in the coupling to the blades sothat all blades of a set are maintained at equal pitch values.

Still another object is the provision of a pitch-adjusting mechanismwhich is independent of rotational direction applied by the drive meansso that starting up from rest position in either a clockwise orcounterclockwise direction is effective to increase the blade pitch fromminimum to maximum.

A further object is the provision of a simple, lightweight and eflicientimpeller blading system and an associated enclosure which requires noexternal agency or mechanism for preventing the forward or backward flowof gas or fluid therethrough in the stationary blade condition, andwhich requires no external control to effect a sealing action in therest condition.

With these and other objects in view as well as other advantages whichwill become apparent in a discussion of the improved construction, theinvention consists in several novel features and combinations thereofset forth in the appended claims, wherein it will be understood that theseveral constructional elements constituting the invention may be variedin proportion and arrangement without departing from the nature andscope of the appended claims.

To enable others skilled in the art to comprehend the underlyingfeatures of this invention that they may embody the same by suitablemodifications of structure and relation of parts to effect the variouspractical applications contemplated for the invention, the followingdescription is to be read in conjunction with drawings showing apreferred embodiment of the invention, namely:

Fig. l is a front view of the impeller and enclosure showing the generalarrangement of the embodiment as applied to an exhaust or ventilatingfan;

Fig. 2 is a sectional view of the impeller and enclosure taken on the'line 22 in Fig. 1 and omitting the pitchchanging mechanism;

Fig. 3 is a side view of the impeller as illustrated in Fig. 1 with theblades in the open or maximum pitch position showing curved blade sealsurfaces on the enclosure;

Fig. 4 is a detailed enlargement of the sectional view through theperipheral seal assembly of Fig. 3;

Fig. 5 is a partial sectional view of the spinner or hub illustratingthe pitch change mechanism;

Fig. 6 is a partial sectional view of a spinner substantially on theline 33 of Fig. 5, showing the detail of the arrangement of bladerotating elements and axial screw actuator;

Fig. 7 is a partial sectional view of a spinner showing the method ofassembling and securing the parts of the spinner cap and base;

Fig. 8 is a sectional view similar to Fig. 5 corresponding to anotherembodiment of the invention;

Fig. 9 is a cross-section taken on line 9-9 of Fig. 3 showing theimpeller shaft and coil springs mounted thereon.

General description of hub Referring to the figures of drawing, apractical embodiment of the invention generally comprises an assembly ofa shaft adapted to be coupled to a drive motor, a hub coaxial with andenclosing blade pitch-adjusting mechanism and journalled on the shaft, aset of blading supported rotatably in the hub having their length andpivot axes substantially perpendicular to the shaft, and an enclosureassociated with a motor housing coaxially mounted with respect to theshaft having sealing flanges co-operating with a seal ring carried atthe outer margins of the blades.

Having regard first to Figures 1, 2, and 3 of the drawing, a propelleror impeller hub is realized as a hollow, somewhat pear-shaped housingwhich is preferably a body of revolution comprising a forward sphericalshell portion 10 assembled with a larger rear hub portion 11, as bymeans of paraxial screw devices 12, to enclose a space generallydesignated as 100. A compression sealing gasket 26 is interposed betweenthe abutting faces .of the two shell portions of the hub to provide adustproof and oil-retaining protective enclosure for mechanism when theparts are assembled. The hub surrounds the end portion of shaft 13 andis captively supported thereon in coaxial relation. Coaxially of the hubbody 11 a bore 27 is provided wherein a cylindric bearing surface 28 ofthe shaft 13 is journalled. A blind bore 49 is formed in the forward hubshell 10 coaxially therewith and opening inwardly to journal the forwardend 50 of the shaft 13 therein. Supported about the periphery of the hubportion 11 are a set of propeller or impeller blades, these beingdesignated 14, 15, 16, and17 in the Patented Oct. 18, 1960 case of thefour-blade assembly depicted. The blades are mounted upon respectiveshafts 18, 19, 20, and 21 disposed substantially at right angles to theaxis of the shaftdfl and iincluding respective reducedxdiameter por-.tions.i.22,i23,124,'and 25 adjacent their innenends. .These reduced'diametenportions as best shownin Fig. 6, are :journalled in tboresextending through zthe spherically shapedpart of shell 11 and.equiangularly spacedabout theiperiphery thereof. Supported uponandsecured-to the terminal portions of the blade pivot axles just describedare the respective collars 29, 30, 31 and 32 which are restrainedagainst axial movement, as by use of grubscrew or similarFfasteningdevices 33, .34, 35, and :36. Thecollars include lateralextensions asfor example respective integral flange.:portions .37, 38,39, and 40, each collar carrying its respective pair of pins-of the sets.ofzpin'pairs 41-42, 4344, 45-46, and 47-48. These pins are aflixed toextend inwardly of their mounting .collar in a direction-substantiallyparallel with the pivot axis ofthe blade shaft associated with thatcollar, and the pins are moreover spaced equidistantlyin oppositedirections along a line passing through the blade pivot axis.

The outermost faces of the collars 29 to 32 inclusive are suitablyshaped to conform with the inside of the .rear shell 11; in a preferredembodiment the inside faces of the shells are machined smooth in theregion surrounding each bore toprovide flat bearing surfaces adequate towithstand centrifugal forces when the impeller .is-rotating.Alternatively the inside of the shells. in the vicinity of each bore inwhich the shafts 22, 23, 24, and 25 are journalled are made sphericaland the outer end of each of the aforesaid collars is convexlyspherical.

The inner face of the forward shell 10 carries axially protruding postsor shaped guides 51 and 52, preferably formed integrally with the shell,and spaced laterally from the bore 49. As will be described later, theseposts serve as ways or guides to prevent rotation of acarrier 53 formingpart of the pitch-adjusting mechanism presently to be explained.

Alternatively the guide may be realized as a cylindric .boss-havingeither internal or external splines or equivalent forms designed toprovide for axial freedom of movement for a guided body whilerestraining relative rotation therebetween. In one embodiment such bosshas a squared shoulder against which the restoring spring may be seated.

The rear shell 11 is machined to provide a stepped bore including theaxial bearing 27 and an annular thrust .bearing disc face 54 concentrictherewith on the inner side of the shell.

Blade pitch adjusting mechanism Primary shaft 13 which is preferablymachined from a single length of rod of steel or other suitablematerial, isformed with a collar 55 adjacent a bearing surface28, .thecollar serving as a thrust bearing member in association with the discface 54 to prevent outward axial 1movernent of the shaft. The outer endof the shaft is .of reduced diameter and is finished to provide an axle:50.journalling in the end bearing 49 by which it is also restrainedagainst forward axial movement. Between the small end and the collar theshaft has a portion 56 formed of intermediate uniform diameter, thisportion being threaded concentrically with the shaft axis. The threadmay be realized in any thread form and in any suitable pitch, preferablyas a fine pitch thread of close tolerance. In applications requiring alarge diameter threaded portion it may be advisable to use aself-centering thread; however in the majority of applications as for-example in space venting fans the thread may preferably "be' NationalFine machine thread. In general as the num- (bet-f threads per inch isincreased the mechanical ad- "vantage of the pitch-adjustingmechanism-is proportionrately increased withthe result that the torqueeffect-for a given loading of the impeller system effective to alter theblade pitch is increased. In some applications a coarse pitch will befound preferable to obtain rapid and large changes in blade pitch.

A body 53, hereinafter referred to as the actuator nut, has an axialbore threaded to mate with the thread of the shaft portion 56, uponwhich it rides. Sufficient clearance is allowed for smooth engagementofthe threaded parts with low friction and a minimum of axial play. Anouter end of the actuator nut hasan integral flange 58 extendingradially of the nut, the flange being milled axially to engage the ways51, "52 in the end shell 10 of the hub. .An inner .shoulder 59 formed onthe flange serves as a support for restraint of the outer end ofcompression spring'60 which is coaxially disposed on the nut 53. Theother end of the spring rests against an apertured flanged disc 61 whichis freely slidable on the cylindric portion of nut '53. The inner end ofthe nut is formed with a circular integral disc flange 62. Pressure ofthe spring 60 against disc 61 forces the latter against pins 41, 43, 45and 47, thereby developing a torque tending to rotate each blade shaftinto a rest position in which the said pins are pressed between thediscs 61 and 62. At this rest position the respective pin pairs such as41 and 42 on collar 37, lie in contact with the front and the back faceof the flange 62.

While a conical spring60 is shown in the drawing, to provide for ashorter fully compressed spring length, the use of straight springs isenvisaged in those applications where the relative compression of thespring need not be large. Between the shaft flange 55 and the reduceddiameter portion 56 there are mounted two opposed flat power springs 63and 64 whose inner ends are suitably secured to the shaft and whoseouter ends are captive on posts 65, 66 secured to the inside of shell11. The coils are restrained and guided by washers 67, 68, and 69, andby spring retainer 70 which engages a groove 71 in the shaft. Tensioningof the coils is arranged to hold the shaft 13 in a rest position atwhich pin pairs such as 41 and 42 are in contact against opposite facesoffiange 62.

Blading and seals As has previously been set forth the impeller bladingis aflixed to shafts 18, 19, 20 and 21. As will be most directlyapparent from Figure 8, the shafts, which may conveniently be realizedfrom rod stock, are cut away to form approximate semi-cylindersextending outwardly from the base portions 72, 73, 74 and 75, which areleft in their original'rod diameter size to prevent axial play of theshafts. The blades are realized preferably as rigid bodies of sheetmetal or other material having suitable characteristics and in the caseof metal may be affixed by rivets or by spot-welding to the fiat facesformed on the shafts.

Referring additionally to Fig. 1, the outline of each blade as viewedfrom the front is seen to include a leading edge 76 which roundssmoothly into the circular outer edge 77, a trailing edge 78 lyingsubstantially along a radius, and a circular inner edge 79 conforming tothe periphery of the hub. In the drawings Figs. 1, 2 and 3 the rotationof the blade assembly is anticlockwise and the rotation of eachindividual blade is such that leading edges move toward the front orviewing position while the trailing edges swing away oppositely, withincreasing blade pitch.

The forming and arrangement of the impeller blades is such as to permitthe trailing edge of each blade to lie in close contact with the backsurface of an adjacent blade, the line of contact extendingsubstantially the full length of the blade. The contact line will beobserved to lie at the leading edge of the overlapped blade. The exactshape and number of the blades may be varied considerably; as hereindescribed the blades are essentially concave to the front butareuncurved along any radius through the hub axis, andthe leading edgeportion overof the hub but rests against the inner face of flange 58 ofthe nut 53. In the centered rest position as illustrated,

pin 42 is gripped between integral flange 62 and the right, the pin 41will experience a rotatory displacement to the left causing spring 60 tobe compressed further, the deflection in the Fig. embodiment being twicethe displacement of flange 62. In the embodiment of Fig. 8 it will beobvious that the spring 60 will be compressed equally with spring 69. Atthe same time, due to the relative rotation of shaft 13 as has beenindicated, coil spring 64 will wind up and spring 63 will unwind anequal and opposite amount. There will consequently be a torque on hubpart 11 transferred by the pull of spring 64 on post 65, tending to spinthe hub and assembly to follow the shaft rotation.

Dynamic operation of blade-adjusting mechanism Referring particularly toFigs. 1, 5, 6, and 8, the operation of the mechanism contained withinhub space 100 will be discussed in the following description. Let it beassumed that there is applied to shaft 13 a torque tending to rotate theblading anticlockwise as viewed in Fig. 1. For this direction ofrotation the blading if opened would tend to urge air through theaperture in housing 95 from the front to the rear. Inasmuch as the usualdrive motor means 93 accelerate from rest condition to driving speed ina relatively short interval of time, the inertia of the hub and bladeassembly will resist rapid increase in rotational velocity. Accordingly,flat spring 64 will wind up as shaft 13 rotates relatively to the huband spring 63 will unwind. At the same time the relative rotation ofthreaded shaft portion 56 within actuator nut 53 will cause the latterto be drawn axially to the right in Fig. 5 away from shell portion 10,moving pins 42, 44, 46 and 48 to the right under pressure of flange 62.The rotation of collars 37, 38, 39' and 40 will be opposed by thereciprooal opposite displacement of pins 41, 43, 45 and 47 whichcompress spring 60 by forcing disc 61 to the left. It will be apparentthat the extent of relative rotation of the shaft 13 with respect to thehub assembly is limited by the loading due to winding of coil spring 64and the compression of spring '60. After a certain angular relativerotation has occurred the coupling between the hub and shaft 13 will berelatively rigid and the hub takes on the rotational speed of the shaft,with the blading opened to its greatest pitch. As soon as the drivingsource has reached its equilibrium speed due to the load, the loadingdue to acceleration of the hub assembly substantially disappears, withthe result that-a slight decrease in blade pitch will possibly occur dueto unwinding of fiat spring 64 and a winding up of spring, 63. At thesame time axial decompression-of spring 60 in Fig. 5, or of springs 60and 60' in Fig. 8; brought about by the decrease of blade pitch, reducesthe loading. The resistance or drag ofthe moving blading against the airstream developed and the reaction forces due to accelerating the streamremain effective to hold the blading open at an equilibrium pitchsetting.

The extent of drag forces on the blading and the torque effect tendingto hold the blades open will in general be determined by the airfoilcharacteristics of the blade forms chosen. Where. the center of pressurelies between the leading edge and the blade pivotshaft over the workingrange of blade pitch'angles there will be'a'couple tending to increasethe plate pitch.

With conventional drive motors of shaded pole induction type or serieswound brush type their equilibrium rotational velocity under variableloading is generally related inversely with the magnitude of theloading; consequently where such drive is employed with the bladepitch-adjusting mechanism according to the invention fluctuations inapproach velocity of the air stream tending to decrease the loading onthe blades will co-operate with the regulation characteristic of themotor to maintain a relatively steady fan spin rate.

T he embodiments in Figs. 5 and 8 may be used in those applicationswhere it is desired to move air or gas in either direction through theaperture in housing for example, where the flow is desired from the rearor motor side towards the front the direction of motor drive will bereversed by means not forming any part of this invention, causing theblading to spin clockwise in Fig. 1' view. Under this condition theflange 62 compresses spring 60 as it urges pins 41, 43, 45 and 47 totheleft against disc 61, and flat spring 63 winds up to an equilibriumcoupling condition, while the blade pitch increases as described before.

If the direction of drive is again reversed while the blade assembly :isspinning to drive air from the rear to the front, the actuator nut53-will be rapidly axially moved through the zero blade pitch condition,thereby arresting the flow of air, and the same blade pitch angle asbefore will be quickly re-established as the coupling between shaft 13and the hub assembly becomes more firm.

In some applications it may be acceptable to permit shaft 13 to rotate alarge number of revolutions beforeone of the spiral springs *63 or 64 isfirmly wound up to provide'arigid coupling. Where the actuator nut 53may travela considerable amount, sufficient leeway must be providedbetween the end of the shaft thread 56 and the nut travel limit toprevent jamming, or a suitable cushion or stop may be provided to arrestthe nut.

I claim:

1. A variable blade pitch impeller comprising a drive shaft having athreaded portion, a hollow hub enclosing said threaded portion andjournalling said drive shaft therein, a plurality of impeller bladeshaving radial blade support shafts journalled in said hub to turn aboutrespective blade shaft axes, collar means fixed to each blade shaftwithin the hub each carrying a pair of pins extending'inwardly parallelwith respective blade shaft axes and spaced oppositely from said axes, aflanged actuator nut threadedly engaging said drive shaft reciprocablein guide means in said hub preventing relative rotation of said nut;said-flange extending between respective pins of each pin pair, springmeans biasing one pin of eachpin pair against said flange, and resilientmeans coupling said hub with said drive shaft whereby when said hub andsaid drive shaft are disposed in predetermined angular relax-t tion saidflange is in contact with both pins of each pin pair to hold said bladesin a reference pitch setting.

2. Avariable blade pitch impeller as in claiml wherein said resilientmeans comprise a pair of opposed spiral torsion springs coaxial withsaid drive shaft and each having one end fixed thereto and its other endfixed to the hub, said springs being wound in opposite senses.

3. An impeller organization comprising a drive shaft having a lengthportion threaded adjacent one end, a hollow hub journalled for rotationupon the shaft to enclose said portion, a plurality of blades having:blade shafts radially arranged about the hub and having their inner endsjournalled for rotation'in said hub about axes lying in median planestransverse to said blades, 2. pair of crank pins extending within saidhub and secured to the inner end of each blade shaft, said crankpinsbein'g spaced equally on opposite sides of a blade axis, torsionspring means yieldably coupling said hub with said drive shaft forrotation together in either direction and toestablish a referenceangular relation therebetween said hub and lapped by an adjacent bladeis curved forwardly outwardly while the trailing edge is curvedsimilarly forwardly. It is to be understood that a blade mayalternatively be formed on dies conforming to the surface of a cylinder,of which the generating line moves about an axis normal to and passingthrough the drive shaft axis.

The outer ends of the blade shafts are journalled in rapective cups orsockets 80, 81, 82 and 83, secured in any suitable manner to the backsurface of an annular disc portion 85 which lies radially inwardly of acarrier ring 84 surrounding the blading and forming part of a rotativeseal. Lying radially inwardly of the disc 85 is a discontinuouscylindric band 86 whose axial length varies around the circumference andwhich extends in certain regions more to the forward side of disc 85than on others. A radially inwardly directed blade-edge seating flangegenerally designated 87 is integral with band 86 and is curved from theplane of disc 85 to conform with the curvature of blade edges 77. InFigure 2 the flange areas 88 are displaced a maximum distance forwardlyfrom the disc 85 while at the discontinuities of the band 86 in theimmediate proximity of sockets 80, 81, 82, and 83 the Width of band 86and the displacement of the seal flange 87 are approximately equal tothe blade material thickness. In general, it will be a design choice toaxially shift the relation of flange 87 with respect to disc flange 85,for example to dispose areas 83 and the socket areas equally andoppositely from flange 85.

Flange 87 is preferably formed by a forming die shaped between areas 88to conform to a surface of a cylinder whose axis is normal to the axisof shaft 13 and disposed forwardly of the hub. The outer margins 77 ofthe blades are therefore preferably formed with a slight forward arcuatebulge conforming to the overlap of a rearwardly disposed area of flange87.

Each blade lies in its rest position with that part of its outer edgewhich extends between the support shaft and the leading edge lying incontact with the forward side of flange 87, while the remainder of theouter edge lies in contact with the rear side of the flange 87. In thevicinity of the junction of the trailing and outer edges of each blade,a depressed tab 89 is formed integrally with the blade having a maximumdepth measured at the trailing edge equal to the thickness of the flangearea 88. The depth tapers to zero along the shoulder which forms theboundary between the tab and the unformed body of the blade. The contourof this shoulder substantially follows the outline of the flange area88, and is preferably produced by a forming die, or alternatively bypartial shearing in a die. The front side of the tab lies in closecontact with the rear face of the flange area 88 to provide an effectiveseal, while the rear side of the blade overlaps the flange area 88 tocomplete the peripheral seal.

As previously indicated the radial seal between adjacent blades is alonga line of contact which extends to the shoulder of the tab 89. Anyleakage at the outer edges of the blading is therefore limited to therelatively narrow gap between the shoulder of tab 89 and the flangeoutline at the area 88. Such leakage may be reduced to a very low valueby careful design and precision.

At the inner edges of each blade a somewhat similar peripheral sealprovision is made, which is best understood by reference to Fig. 7. Adiscontinuous peripheral flange comprising segments 90, 91 is formedintegral with and disposed about the hub 11. That part of the inner edge79 of each blade which extends between the shaft and the blades leadingedge lies to the front of and in contact with the seal segment 99. Theremainder of the inner edge lies to the rear of and in sealing contactwith the seal segment 91. The segmental lengths are so arranged thatonly sufficient clearance remains between the end of a segment and ablade support shaft 13, 19, 29 or 21, to allow for free shaft rotation.A relative axial 6 displacement is provided between the end of segmentadjacent to an end of segment 91, parallel to the axis of shaft 13,equal to at least the blade thickness.

A depressed tab 92 is formed at the junction of leading edge 78 andinner edge 79 integrally with each blade, with a depth measured normalto the trailing edge substantially equal to the thickness of segment 91,and gradually tapering to zero along the shoulder of the depression,which conforms to the outline of segment 91. Each of the segments 90 and91 may be, and preferably is, warped axially to protrude forwardly atits mid-length position, or more specifically is formed with a ridgelying in line with the blade trailing edge, to conform with bladecurvatures.

Referring again to Fig. 2 the blade assembly including the ring 84- andannular disc element 85 will be seen to be located with respect to anenclosure by a support frame 94- in which a motor 93 is mounted. Theexact form of the frame is not critical and may comprise, for example, amesh of wires or rods of adequate strength and rigidity secured to theenclosure and to the motor mounting. Motor 93 may be of any suitabletype having a drive shaft 102 upon which fan shaft 13 may be coaxiallyfitted and secured in drive relation.

Ring 84- is disposed coaxially within an annular cavity formed betweenan inner flange 97 of the enclosure 95 and a formed ring 96 secured tothe back of the enclosure. It will be apparent that a labyrinthalpassage is thereby provided to restrict flow of air or fluid around theedge of the ring 84. Preferably the ring 96 is flanged reversely with aforward disc flange 98 extending radially outwardly and a rearward discflange 99 directed parallelly with the disc 85. The radial length of theflange 99 is such that a clearance remains between the outer ends ofsockets 80, 81, 82 and 83 and the inner margin of the disc 99. Betweenthe flange 98 and the enclosure 95 a resilient gasket 101 may preferablybe interposed at the time of assembly and the parts are secured togetherby any suitable means, for example by metal screws or bolts and nuts.

The seal ring 84 with its integral disc flange 85, cylindric flange 86,and blade edge seal 87, may preferably be realized by a stamping anddrawing step employing sheet metal stock. Alternatively injectionmoulding or diecasting processes may be employed where a one-piece bodyis desired. Similarly, flange ring 96 may be stamped from light guagemetal or may be realized by any other conventional process of adequateprecision.

In applications where the flow of gas or fluid must be relativelycompletely prevented or where the head existing between opposite sidesof the impeller is relatively large in the stationary closed-bladeposition, the fabrication of the various parts will require to becarried outwith a greater regard to rigidity and precision of fits. Thesurfaces of the blading and all surfaces of the seal flanges :may becoated with a resilient film of a soft rubber or plastisol, preferablyby dipping or by spraying before assembly. In certain fluid pump andcompressor applications the inner surface of the rotary ring 84 will bearranged to actually ride against the outer surface of the panel flange97, to produce a sleeve bearing type of seal. Where an anti-frictionlarge bore type of ball race bearing (not shown) is provided between therelatively rotating elements and carries its own seal, the flanged ring96 may be eliminated.

An alternative embodiment is shown in Fig. 8 wherein means are providedfor centering the actuator nut 53 more positively to achieve arelatively more rigid closed-impellor position. In the sectional view itwill be apparent that the mechanism housed within the hub is similar tothat of Fig. 5 with the primary difference that a second compressionspring 60' is provided, retained between a further axially movable disc61' and an end flange 57 on the actuator nut 53. It will also be notedthat the outer end of spring 60 is not seated against any part driveshaft are at rest, actuator nut means engaged with said threaded lengthportion guided in said hub for axial reciprocation when said hubover-runs said drive shaft in either direction, said nut having anintegral disc flange extending radially between crank pins of each pairwhereby to swivel said blades from substantially zero pitch settingcorresponding to a reference nut position along said drive shaft whensaid hub and drive shaft are at rest to a working pitch setting whensaid drive shaft turns in said hub in either rotational sense, and meansresiliently biasing corresponding crank pins of each pair to bearagainst one side of said flange.

4. An impeller organization as in claim 3 wherein opposite crank pins ofeach pair are resiliently biased in axial directions toward each other,and wherein said torsion spring means comprise a pair of spirally woundsprings each having their one ends fixed to the drive shaft and theirother ends fixed to said hub, said springs being wound in oppositesenses.

5. In a variable pitch impeller organization the combination of a hollowhub, a drive shaft journalled for rotation in said hub and having athreaded portion enclosed therein, means yieldably coupling said hubwith said shaft to establish a reference angular relation therebetweenwhen at rest, a plurality of impeller blades having axles whereof theinner ends are swivelled in said hub about axes substantiallyperpendicular to and equiangularly spaced about said drive shaft, a pairof crank pins fixed to each of said inner ends, the pins of a pair beingspaced equally and oppositely from the respective blade axes, an axiallyreciprocable rotationally restrained nut engaged with said threadedportion of said shaft for relative screw rotation thereon when saiddrive shaft over-runs said hub in either rotational sense, a coaxialdisc flange carried by the nut disposed between crank pins of each ofsaid pairs and occupying a reference axial position along said shaftcorresponding to said rest angular relation of said hub and drive shaft,and means biasing a corresponding pin of each pair against a side ofsaid flange whereby to establish a zero pitch blade setting when saidhub and drive shaft are at rest and whereby displacement of said nut inopposite axial directions from said reference axial position effects theswivelling of said blade axles in the same direction to increase theblade pitch.

6. A variable blade pitch impeller as in claim 5 wherein said yieldablecoupling means comprise a pair of opposed torsion springs coaxial withsaid drive shaft each having their one ends joined with said drive shaftand their other ends joined with said hub, said springs being wound inopposite senses.

References Cited in the file of this patent UNITED STATES PATENTS Re.18,957 Gobereau et a1 Sept. 26, 1933 913,364 Crowhurst Feb. 23, 19091,610,010 Johnson Dec. 7, 1926 1,656,019 Roberts Jan. 10, 1928 1,689,735Losel Oct. 30, 1928 1,765,091 Morris June 17, 1930 2,133,485 Sherman etal. Oct. 18, 1938 2,133,486 Sherman et al. Oct. 18, 1938 2,200,952Farrell May 14, 1940 2,225,209 Dewey- Dec. 17, 1940 2,383,001 Mader Aug.21, 1945 2,383,002 Mader Aug. 21, 1945 2,383,004 Mader Aug. 21, 1945FOREIGN PATENTS 70,616 Denmark Jan. 30, 1950 299,479 Switzerland Aug.16, 1954 703,458 Great Britain Feb. 3, 1954 1,040,606 France May 27,1953

